The present invention relates to a method for photopolymerizing a monomer mixture of lens-forming monomers to form a lens, such as a contact lens or an intraocular lens. The monomer mixture is cured by exposure to a light source including light in the visible region of the spectrum. Alternately, the monomer mixture is cured by exposure to a UV radiation source even when the monomer mixture includes a UV-absorbing compound.
Lenses such as contact lenses or intraocular lenses may include a UV absorbing agent in the lens to absorb light in the ultraviolet region of the spectrum, more particularly, to absorb light in the region of about 200 to 400 nm and, especially, about 290 to 400 nm. Representative UV absorbing materials for such lens applications are described in U.S. Pat. No. 4,304,895 (Loshaek), U.S. Pat. No. 4,528,311 (Beard et al.) and U.S. Pat. No. 4,719,248 (Bambury et al.).
Generally, such lenses are formed by free radical polymerization of a monomer mixture including desired lens-forming monomers, usually in the presence of heat (thermal polymerization) or a light source (photopolymerization). One particular method for producing contact lenses involves thermal polymerization of the initial monomeric mixture in tubes in a heated water bath to provide rod-shaped articles, which rods are then cut into buttons, the buttons then being lathed into contact lenses; such methods for forming lenses including a UV absorbing agent are illustrated in the aforementioned U.S. Pat. Nos. 4,304,895 (Loshaek) and 4,528,311 (Beard et al.). Other methods involve casting the lenses directly in molds, wherein the monomer mixture is charged to the mold and polymerized by exposure to ultraviolet (UV) radiation.
Among photopolymerization processes, UV curing (i.e., exposure of the monomer mixture to radiation mainly in the ultraviolet region) of the monomer mixtures has proved very effective. However, for lenses including a UV absorbing agent, problems are encountered when attempting to cure the monomer mixtures since this agent absorbs UV light, thus diminishing the amount of UV light available to effect polymerization and resulting in ineffective or uneven curing of the monomer mixture.
It is also possible to effect photopolymerization using a light source also including light in the visible region of the spectrum, although light in this region is generally less efficient in effecting polymerization of conventional lens-forming monomer mixtures than UV curing. It would be desirable to provide a method whereby lenses including a UV absorbing agent can be effectively photopolymerized by free radical polymerization employing light energy in the visible region of the spectrum or UV radiation.
The invention provides a method for photopolymerizing a mixture of lens-forming monomers to form a lens. In addition to the lens-forming monomers, this mixture comprises an initiator of the formula: 
wherein:
Ar represents an aromatic radical;
Ra represents a secondary amino radical;
Rb represents an ethylenically unsaturated radical or an aromatic radical; and
Rc represents a secondary amino radical.
The monomer mixture is exposed to polymerization-inducing radiation, particularly visible light or UV radiation, to cure the monomer mixture. The monomer mixture may be charged to a mold having a molding cavity with a desired lens shape and cured therein. The method is useful for monomer mixtures that include a UV-absorbing compound.